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Sept. l0, 1940. LE RoY J. LElsHMAN X-RAY STEREOSCOPIG MEANS AND METHOD Original Filed Oct. 5, 1935 4 sheets-Sheet 1 Sept. l0, 1940. LE ROY J. LElsHMAN 2,214,621

X-RY STEREOSCOPIC MEANS AND METHOD 4 sneet-sneet 2 Original Filed Oct.A 5, 1935 /NVE/vO/P; y g my Mm Sept. l0, 1940. LE: ROY -J. I ElsH'MAN X-RAY STEREOSCOPIC MEANS AND METHOD Original Filed Oct. 5, 1955 4 Sheets-Sheet 5 //V VE'N TOR.'

Sept. l0, 1940. LE ROY J. I ElsHMAN X-RAY STEREOSCOPIC MEANS AND METHO) Original Filed Oct. 5, 1935 4 Sheets-Shee*` 4 QW/[N705: my, fr MAM Patented Sept. 10, 1940 Fries l X-RAY STEREOSCOPIG MEANS AND METHOD Le Roy J1 Leishman, Los Angeles, C'alif.

Application October 5, 1935, Serial No. 43,688

` f Renewed February 13, 1940 9 Claims.

The invention herein described relates to stereoscopic iiuoroscopy and radiography. Some of its objects are: first, to provide practical means for varying the distance between the required two sources of X-rays; second, to afford simple means whereby the separate images produced by the X- rays from these two sources may each be made visible to a diierent eye; third, to make it pos- 'sible to control the corresponding shutters for both X-ray tubes from a common control; fourth, to provide means for producing a second image in thespace occupied by the grid lines that cross'. an X-ray picture or fluoroscopic shadowgraph; and iifth, to provide a simple stereoscope iorviewing such stereoscopic pictures. Other objects will appear as the specification proceeds.

In the drawings:

Fig. 1 shows diagrammatically an arrangement whereby two iluoros'copic images are produced in alternate strips by means of a grid opaque to X-rays and obscured each from a different eye by means of a second grid opaque to ordinary light.

Figs. 2 and 3 illustrate a modification wherein a vibrating Bucky diaphragm or Lysholm .grid causes the two X-ray images to fallin alternate strips during alternate halves of the cycle oi the alternating current'operating the'X-ray tubes and the grid vibrating mechanism.

Fig. 4 shows a transparent screen of alternate differently colored strips. In one modification of the invention, this colored screen replaces the .grid that is opaque to ordinarylight in Fig; 1. f

Fig. 5 shows an assembly on which theftwo X- ray tubes may be mounted, together with the mechanism for operating thevshutters and varying the distance between the tubes.

Fig. 6 is a side elevation of Fig. 5, with certain parts omitted for the sake of clearness, and showing an X-ray tube'mounted in its supports.

Fig. 'l shows part of the control mechanism for the moving parts illustrated in Fig. 5.

Fig. 8` is a plan View of part of the mechanism wherebythe distance between the tubes is automatically varied in accordance with the position of the fluoroscopic screen, and of a remote control for the tube shutters.

Fig. 9 is a front elevation of the outer end of the control mechanism shown in Fig. 8.

Fig. 10 is a front elevation of the back end of vthe mechanism shown in Fig. 8, taken along line 65-66, Fig. 8, and shows in addition the various elements whereby motion is transmitted to the movable parts illustrated in Figs. 5 and 7.

Fig. y11 shows diagrammatically a double Kerr (Ol. Z50-60) cell assembly with additional parts whereby the right and left eyes may see through their associated optical systems during alternate halves of the cycle of the actuating current.

by side withl unlike ends together. The anode of one tube is connected to the cathode of the other by wire l, which is in turn connected to the high potential wire t. "The opposite ends of these tubes, not shown in the iigure, are also connected together and vto the other side of the high voltage line. X-rays romlthese tubes! fall on the fluorescent screen C` through the grating D, the lines vof which are so spaced with relation to the screen C and the tubes A and B that the rays a from tube A pass between the strips of the grating D and fall on theA portions of screen C that are shielded by grid D fromthe rays b from tube B, as shown in the gure. E is a grating consisting In Fig. l, A and Bv are X-ray tubes placed side 5 of linesr or strips alternately opaque andtrans- 20 parent to ordinary light.l rlhe spacing of these lines and' thesdistance of grating El from screen C are such that the right eye R sees the portion of the screen C' made iiuo-rescent by the rays a from tube A, andthe left eye L sees thestrips of screen C that'are made to fluoresce by rays brom tube B. Other details of Fig. 1 Awill be. eX- plained Afurther on in this specification.

Ii a patient to be examined fluoroscopically is f placed between the tubes and grid D, the images producedby the X-rays on screen Cwill be slightly different, due to the distance between the targets where the X-'rays originate. This diierence is well known in stereoscopic X-ray work. Inasmuch as these images lie in alternate strips, the grating E hides one image from the right eye and the other image from the left eye, thus permitting each eye to see one image only. Due to the difference between these images, the effect is stereoscopic, and the shadows appear to be three- 40 dimensional objects. The observer thus has the sensation of looking right into thebody. The

grating D may consist of a self-supporting grid oi lead or other substance opaque to X-rays, or of a sheet of Bakelite, aluminum or other material rk45 transparent to X-rays having'grooves that are etched, engraved-or pressed into the surface and then iilled in with a material through which X- rays cannot pass, such as powdered lead in a suitable base. A satisfactory grid of this nature may also be made by Stringing wire between two parallel notched supports, as is done with the warp in certain vkinds oi" weaving.

It is well known in radiography and fluoroscopy that the increased sharpness of an'v image produced with a Bucky diaphragm or Lysholm grid more than compensates for the grid lines on the i'luoroscopic screen or X-ray plate. By -moving the grid in synchronism with the alternate action of two X-ray tubes connected as in Fig. 1, it is' possible to produce two images upon the same surface, each picture occupying the position of the grid lines across the other picture. This is accomplished by theapparatus illustrated in Figs. 2 and 3, in which D2 is a grid composed of lead or similar strips of material with intervening spaces having a greater depth than width. F is one of a series of magnets or solenoids for attracting the iron member G attached to the grid D2. I-I is one of a plurality of springs for resisting the action of the magnets or other similar electrically operated means. The current that energizes F is a rectiiied current originating in the same alternating current source as that which operates the X-ray tubes, as indicated in Fig. 2. When alternating current from wire 93a passes through wire 93 in the direction indicated by the arrow, it passes through the half-wave rectifier 88, then through wire 9i, magnet F, and wire 92, which connects to 92a, leading to the A. C. source. During the opposite half-cycle of the alternating current, no current will flow through the circuit just described, because it will be in the wrong direction to passv through rectiiier 88. Alternating current. from wires 92a and 93a is also used to operatethe high voltage transformer IIIIJ, whose `secondary is connected by wires Iil and III'I to the X-ray tubes A and B. Because of the wellknown rectifying action of these tubes, they operate on opposite halves of the alternating current cycle. It will thus be evident that during one half of the alternating current cycle, F will be inoperative while the rays from one of the tubes pass between the lead strips of grid D2, leaving dark lines I beneath said strips on screen C as indicated in Fig. 2. During the next half cycle, F will be energized, thus causing grid D2 to move to the position shown in Fig. 3, leaving the previously protected parts of the screen now exposed to the other X-ray tube which is now in operation while the rst tube remains inoperative on this half of the cycle.

The tubes A and B are of course at some distance from screen C, as indicated in Fig. 1, but they have been placed much closer in Fig. 2 merely to save space; and it should be understood that the electrical relationship between the tubes and the grid-actuating means, F, is the only feature of the tubes intended to be indicated by Fig. 2.

The necessity for rectifying the current to F can be ob-viated by polarizing F so that it operates only on alternate halves of the cycles of an alternating current. Many other electrically operated means could be provided'to vibrate the grid D2, such as a synchronous motor revolving an eccentric connected to the grid.

If an object to be X-rayed is placed between an assembly like that of Fig. 2 and a pair of X-ray tubes connected and positioned as shown in Fig. 1, and if the current to F is in phase with that which operates the tubes, it is obvious that two different shadows will occupy alternate strips on screen C. By placing a grid like that of E, Fig. 1, in front of screen C, Fig. 2 or 3, these images may Vbe seen each by the proper eye only, and the effeet will be stereoscopic.

Fig. 4 shows a screen of alternate transparent strips of red and green or other suitable colors. Such a screen may be used as a substitute Yfor -screen E in the previous figures. The` coloredv lines are of such Width that those of one color will register with the lines of one of the images on screen C, while the lines of the other image will lie behind the strips of the other color. If the strips of this alternately colored screen are red and green and the observer wears spectacles having one red and one green glass, 'the red strips of the screen will all appear black to the eye wearing the green glass and therefore only the image lying behind the green strips can be seen by this eye. Similarly, the eye Wearing the red glass will be able to see the other image only.

It will be obvious that stereoscopic X-ray pictures may be taken in alternate strips on the same plate by means of modifications of the apparatus just described, thus eliminating the necessity of using two plates with usual plate changers. In such stereoscopic radiography, screen C, Fig. 1 or 2, is replaced by the plate to be exposed.

Such pictures may be viewed by providing a View box withY a grating like E, Fig. l, or with a transparent screen having alternate strips of a different color,`like that illustrated in Fig. 4. In using this latter arrangement, the two eyes must be provided with the colored spectacles described in a foregoing paragraph.

In Fig. 5, J is a supporting plate which may be attached to the tubev carriage by means of holes R. Rods K and L are attached to plate J by the supports lVI and MI respectively, having connecting screws Y4 and Y5, respectively. Plates SI and S2 are suspended between rods K and L by means of rollers Q attached to these plates as shown in Figs. 5 and 6. Shaft N, having a righthand threaded portion 3, Fig. 5, and a left-hand threaded portion 4, is journaled in the supports O and restrained from longitudinal movement by the collars T. Plates 'SI and S2 carry half nuts 5 and E respectively, which are adapted to engage threaded portions 3 and 4 respectively of the shaft N. 'I'he holes RI and R2, Fig. 5, in plates SI and S2 respectively are for .mounting X-ray tubes. This may be done by means of brackets V, Fig. 6, attached to these plates by means of screws or bolts Y. As shown in this drawing, the tube A is clamped between yoke W and support V by means of screws Y2. Plates Si and S2 have windows UI and U2 to permit the passage of X- rays. By turning shaft N, by means to be disclosed later, the threaded portions engage halfnuts 5 and 6, Figs. 5 and 6, causing the plates Si and S2, with X-ray tubes attached thereto, to move to or from a common center, depending upon whether shaft N is turned to the right or left.

To limit the lateral spread of the X-rays passing through windows UI and U2, Fig. 5, shutters ZI, Z2, Z3, and Z6 are movably attached to the plates SI and S2 by means of L-shaped members II, I2, I 3 and I4, attached to the plates, in the manner indicated in Fig. 6. Shutters ZI and Z2, Fig. 5, are provided with arms I5 and I6,'respectively, extending toward the left; and Zd and Z3 with arms I5a and Ilia respectively, extending to the right. Arms I5 and I6 carry pins I'I and I8 respectively, that ride in slots I9 and 20 respectively, in rocker 2I pivoted on pin 22` attached to plate SI. Arms IEa and I'a have pins Ila and Ia respectively, that slide in slots I9a and 20a in rocker 2Ia having "a pivot 22a. y'I'he outward projections of rockers ZI and 2| a are pivotally attached to levers 23 and 23a respectively by pins 24 and 24a. As will be seen in Fig. 7, levers 23 and 23a are pivotally joined by pin 25, which slides vertically in rslot 26 in the upwardly extending part of plate J. A cord 21 attached to pin 25, passesfover pulleys P1 and P8 and also aroundpulley P9, which latter pulley is attached to shaft 23 journaled in the lateral extension of plate J. If shaft 28 is turned to the right, cord 21 will pull up on pin 25, causing levers 23 and 23a to raise the outward arm of rockers 2| and 2m respectively, Fig. 5. Thiswill move the upper arms of these rockers inwardly, along with pins |1 and Via and the associated shutters Z| and Z4. This same movement of the rockers will cause the lower pins I8 and '|8a to move outward, thus pulling shutters Z2 and Z3 against the respectively associated shutters ZI and Z4. It will be Aobserved that turning the shaft 28 to the right closes the shutters, and that the shutters are simultaneouslyopened by turning shaft 28 to the left, andv that this is true regardless of how near plates Si and S2 are to a common center, since the maximum movement of each of these plates is only 21/2 inches.

Inasmuch as the rays from the two X-ray tubes v must fall on approximately the same area of the fiuorescent screen, the windows UI and U2 must be closer together than theX-ray tubes, as indicated by the relative position of these windows with respect to the holes for mounting the tubes,

, which holes are assumed to be symmetrically arranged in relation to the tubes. More accurately, the center of the opening between shutters Z| and Z must be slightly `to the right of the focal spot on the target in the left tube; and the center of the opening between shutters Z3 and Z4 must be somewhat to the left of the focal spot on the target in the righttube. This difference is indicated in Fig. 1,-in which |0| and |0|a indicate the positions of the focal spots on the targets of the left and right tubes respectively. The distance |62 from the center of the opening between shutters Zi and Z2, and the center of the openingbetween the other pair of vshutters Z3 and Z4, is less than the distance |03 between the focal spots |6| and lilla.

y Shutters 29 and 39 operate vertically, and are long enough to cross both windows UI and U2. Shutter 29 is attached to cord 3| `at 32 and 32a.

Beginning at point32, cord 3i passes downward and around pulley Pi, then up and around pulley P2, thence to the right and around pulley 34, Fig. 'f17V which turns freely on shaft 28. From pulley 34, cordv 3| goes to the left to pulley P3, and then downward, as shown in Fig. 5, aroundv pulley P4, thence up and around P5, and finally around pulley P6, and back to .32. The lower shutter 30 is attached .to cord 3| at points 33 and 33a, Fig. 5. If pulley 34 is turned to the right, shutters 29 and 30 will close;` and they maybe opened by turning 34 to the left.

If the frame J is opaque to X-rays, it is neces.- sary to provide it with a window, U3, Fig. 6, to permit the passage of the rays that emerge between the shutters. This window may be wide enough to accommodate the rays from both tubes, or individual vwindows may be used. Toavoid confusion with other lines, no window of this type isshownin Fig. 5.

Figures 8, 9, and Al() illustrate, among other things, an automatic mechanism for increasing the distance between the two X-ray tubes as the fluoroscopic screen is moved away. To plate J is attached two supporting rods, the uppermost of which, 35, is shown in the plan view, Fig. 8. Rod

there is another arm 38, shown in Fig. 9, which is a front elevation of the parts that lie behind line 39-40, Fig. 8. To these arms is attached a plate 4|, which is fastened to arm 36 by means of bolts 42, Ypassing through 36 and tightened in place by nuts 43, Figs.- 8 and 9. Plate 4| is fastened to lower arm 38 by bolts 44 and nuts 45, Fig. 9. 46 is the holein arm 36 which slides along rod 35, Fig. 8, and 41, Fig. 9, is the corresponding hole in arm 38 which slides along a rod like 35, not shown in Fig. 8 because it lies directly beneath 35.

A shaft 48 passes through arms 36 and 38, Fig. 9, and is held in place by collars 49 and 56. Beginning at the lower end, this shaft 48 supports, in the order named, one end of lever 5|, spacer 52, pulley 53, spacer 54, pulley 55, spacer 56, pulley 51, spacer 58, pulley 59 and spacer 66.

These pulleys and lever 5| are all free to turn on shaft 48. Lever 5| is attached to lever 6|, Fig. 8, by pin 62. The other end of lever 6| is attached to shaft 63, Fig. 10, to which shaft is also attached gear 64. Referring to Fig. 10, which is a front Aelevation of the parts lying behind line -65, Fig. 8, together with additional parts not practical to include in the plan View, it will be seen that shaft 63 is journaled in supports 61 and 68 and held in place by collars 69, 69. As the outer end of lever 6| approaches plate J, shaft 93 and gear 64 turn in the direction indicated by the arrow on gear 64, causing gear 19, shaft 3 and gear 1 to turn in the direction indicated by the arrow on gear 1, which in turn rotates gear 6 in the direc- 'iso tion of the arrow shown thereon, thus turning -attach a flexible shaft directly to shaft N so that the distance between the X-ray tubes may be controlled at the will ofthe operator from any remote point by means of a knob on the opposite end of the flexible shaft.

The shutters for the tubes may be controlled from the assembly attached to arm 36, Figs. 8 and 9. Knob 1|, Fig. 8, and pulley 12 are both attached to shaft 13, journaled in plate 4|. Shaft 13 passes through knob 14 and tube 15, which is attached to knob 14. Tube 15 passes through plate 16 and is attached to pulley 11. Plate 16 is attached to arm 31 and to another arm directly below 31 which therefore does not show in the drawing. ,Knobs 1|` and 14 control the shutters by means of the cords 21 and 3|, which in this case are long enough to extend `over a system of pulleys, (similar to those used on dental drills) to pulleys 12 and 11 respectively, which are shown in Figs. 8 and 9. In this modifi-cation, pulleys P9 and 34, Fig. '1, are omitted, and the following system is substituted: Cord 21, where it would otherwise pass over pulley P9, now passes beneath the substitute pulley Pila, Fig. 19, then around pulley 59h and thence around pulley 59a, Figs. 8 and 9, which latter pulley is free to turn on pin 62. From pulley 59a, Figs. 8 and A9, cord 21 passes around pulley 59, and then around pulley 12, pulleys 53 and 53a, Fig. 9, 53h and 53e, Fig.A 10, from whence it passes to pulley PB, Fig-J1.- r.From

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here back to pulley P9a, cord 2l follows the course originally described. It will thus be evident that shutters Zl, Z2, Z3, and Z4, Fig. 5, can be controlled by knob ll, Fig. 8, which is attached to pulley l2 by shaft '13. When pulley 39, Fig. '7, is eliminated to permit the remote operation of Shutters 29 and 39, cord 3|, after leaving pulley P2, passes over pulley 34a, Fig. 10, around pulley 51h, Fig. 10, then laround 51a, Figs. 8 and 9, pulleys 51, ll, 55, and 55a, Fig. 9, and 55h, Fig. 10, from whence it follows the course originally described. Inasmuch as pulley Tl, is connected to knoblll, by tube 15, as shown in Fig. 8, it follows that shutters 29 and 3|) may be controlled by knob '14.

If it is not desired to control the vertical and lateral shutters from a remote point, pulley 34, Fig. 7, may instead be connected to a tube and knob like 'I5 and 'M respectively, Fig. 8, and pulley P9, Fig. 7, may be connected to shaft 28, whichmay be extended through the tube and connected to a knob like ll, Fig. 8, in a manner well known in the art. l Member '18, Figs. 8 and 9, is fastened between plates 4| and '|8'by screws '|9. Shaft 88 passes through member '58, and to this shaft are attached arms 8| and 82, by means of screws 83 and 84, respectively. To the other end of arms 8| and 82, the holder for the luoroscopic screen is attached in any of the ways well known in the art and therefore neither illustrated nor described here.

Inasmuch as X-ray tubes A and B, Fig. 1, emit X-rays on alternate halves of the cycle of the A. C. current, the images that should be independen'tly viewed by the right and left eyes are not simultaneously present on the screen C, but alternate with the operation of the tubes. 'I'his has made it possible, in the past, to use synchronous shutters to block the vision of the right and left eyes alternately to prevent them from seeing the images intended for the opposite eyes. In addition to new means already described for attaining this same end without the use of moving parts, another novel method is to provide each. eye with a Kerr cell and associated members and energize the Kerr cells alternately by an A. C. current in phase with that which operates the X-ray tubes. Such an arrangement is illustrated in Fig. l1, in which 85 and 85a are Kerr cells, 88 and 86a are polarizers for polarizing the incident light rays, and 8l and Sla are analyzers each capable of adjustment with respect to its cooperating polarizer either to transmit or reject the light polarized by the associated polarizer. These cooperative functions of polarizers and analyzers are well-known in the construction of polariscopes, which are widely used, and in the Kerr cell units as employed in television and telephotography. 88 and 88a are rectifying means whereby cells 85 and 88a are operated on alternate halves of the cycle of the same A. C. current. Current from transformer |89, passing through Wire 89, in the direction of the arrow, will pass through wire 98 and rectifier 88, but will be in the wrong direction to pass through 88a. After leaving rectifier 88, said current passes through wire 9|, cell 85, wire 92 and wire 93 back to the transformer. During the other half of the cycle, the current from `wire 93 will pass through wire 92a, (in the direction of the arrow) cell 85a, wire 9| a, rectifier 88a, wire 90a, and then through wire 89 back to the transformer in an opposite direction to that during the half of the cycle when 85 was energized through the rectifying action of cell 88. Members 94 and 95, and 94a. and 95a support the Kerr cell assemblies, which are paired together by means of brackets 96 and 91, attached to members 95 and 95a by screws 98 and 98a respectively. L and R are the right and left eyes respectively, looking through the cells along lines 99 and 99a respectively.

It is possible, with such Kerr cell assemblies, to arrange the analyzers so that light passes only when the cells are electrically energizedmr when they are not energized. In the arrangement shown in Fig. 11, it is immaterial which adjustment of the analyzers is used, providing both analyzers are adjusted the samethat is, so that light passes through whichever cell receives the charge, or fails to pass through whichever one is energized. It will be assumed, however, that the adjustments have been fixed so that light will pass through the charged cell. When current passes through rectifier 88, as is the case during half of the cycle of the A. C. current, the left assembly represented by 8l, 85 and 86 becomes transparent, and the left eye L is able to see through the assembly along line 99; and during the opposite half of the cycle the right eye sees through assembly 81a, 85a and 86a along line 99a. Inasmuch as these cells are operated by alternating current in phase with that operating the X-ray tubes, the polarity is adjusted'so that the right and left eyes see when the left and right tubes, respectively, are operating, thereby carrying out the same objective as that achieved by grating D and E in Fig. 1.

It is obvious that various modifications may be made from the embodiments of the invention herein described without departing from the spirit of the invention.

My claims are:

l. In X-ray apparatus, a combination including a supporting element; two members movably mounted on said element, each member carrying an X-ray tube and a pair of laterally movable.

shutters; means for moving said members in opposite directions simultaneously; and means for moving the shutters in each pair simultaneously in opposite directions simultaneous with the corresponding movement of the shutters in the other pair.

2. In X-ray apparatus, a combination including two X-ray-tube-carrying members; means for moving said tube-carrying members in opposite directions simultaneously; a pair of shutters movably mounted on each tube-carrying member; means for moving the shutters in each pair simultaneously in opposite directions simultaneous' with the corresponding movement of the shutters in thev other pair; the distance from the adjoining edges of one pair of shutters when closed to the adjoining edges of the other pair of shutters when closed being less than the distance from the focal spot on the target of one tube to the focal spot on the target of the other tube.

3. In X-ray apparatus, a combination including a supporting member; two supported members each carrying an X-ray tube and a pair of laterally movable shutters;I manually controllable means for moving said supported members' in opposite directions simultaneously; means for moving the shutters in each pair simultaneously in opposite directions simultaneous with the corresponding movement of the shutters in the other pair; the distance from the adjoining edges of one pair of shutters when closed to the adjoining edges of the other pair of shutters when to X-rays, said grid interposed closed being less than the distance from the focal spot on the target of one on the target of the other tube.

4. In X-ray apparatus, a co bination including: a source of alternating current; two X-ray tubes adapted to operate on opposite halves of the cycle of said alternating current; a surface that fluoresces when exposed to X-rays; a grid of X-ray resistant strips interposed between said surface and said tubes;.and electrical means for vibrating said grid in synchronism with the operation of said tubes; said grid consisting of parallel strips opaque to X-rays, said strips having a spacing substantially equal to their width.

5. In X-ray apparatus, a combination including: two alternately operative sources of X-rays;

a surface that fluoresces when exposed to X-rays; a grid comprising parallel strips that are opaque between said sources and said surface; electrical means for vibrating said grid; and a grating comprising strips that are transparent to at least part of the rays of the visible spectrum alternating with strips that are substantially opaque to said latter rays; said latter strips adapted to register with said X-ray opaque strips when said grid is at one end of its vibratory swing, and said transparent strips adapted to register with said X-ray opaque strips when said grid is at the' other end said surface interposed of its vibratory swing; between said grid andl said grating.

6. In X-ray apparatus, a combination includingra source of alternating current; two X-ray tubes adapted to operate on opposite halves of` the cycle of said alternating current; a surface that fluoresces when exposed to X-rays, said surface positioned to receive X-rays from said tubes; and two Kerr cell assemblies eachA comprising a polarizer and an analyzer; said'a'ssemblies adapted to pass light on opposite halves of the cycle of said alternating current so that the fluorestube tc the focal spot g ing two members,

ing a supporting element;

cence on vsaid surface that is caused by the X- vrays from one tube may be seen through onek and the fluorescence of said assemblies only, caused by the X-rays from tubes may be seen through the other only.

7. In X-ray apparatus, a combination includeach carrying an X-ray tube and a pair of laterally movable shutters; a fluoroscopic screen; a movably mounted support for said screen adapted to move in a direction perpendicular to said shutters; and means for the other of said assembly moving said members in opposite directions Simultaneously, said means operated by the movement of said support.

8. In X-ray apparatus, a combination includtwo members movably supported on said element, each of said members ycarrying an X-ray tube and a pair of laterally movable shutters; a supporting structure adapted to move toward and from said shutters; a iluoroscopicscreen carried by said structure;

means for moving said members in opposite directions simultaneously, said meansI operated by the movement of said structure; means for varying the opening between each of the two pairs of shutters simultaneously, said shutter-controlling means operable from a manual control carried by said structure.

9. In X-ray apparatus; a combination including a supporting element; two members movably supported on said element, each of said members carrying an X-ray tube; a structure adapted to move in a direction at right angles to the direction of movement of said members; a fluorescent screen mounted on said structure; and automatic means for moving said members in opposite directions simultaneously, said automatic means operated by the movement of said structure.

LE ROY J. LEISHMAN. 

